“There is no fast for the one who does not make an intention before the Fajr.” (Sunan Nasaa’ee no.2338, Shaikh Zubair Alee authenticated it and said Saheeh)

There the intention should be made in the night.

Imaam Ibn Khuzaimah said,

“In this hadeeth Messenger of Allaah (Sallalahu Alayhee Wasallam) was referring to the obligatory fasts (ie the month of Ramadhan) and not the optional fasts.” (Saheeh Ibn Khuzaimah before no.1935)

The intentions needs to be made daily and one cannot say i intend to fast the whole month of Ramadhan.

Imaam Ibn Khuzaimah estblished the following chapter heading for the Hadeeth,

“Actions are but by intentions…” “It is obligatory to make an intention on the day one intends to fast, before the Fajr Prayer (ie sunrise) everyday. In opposition to the individual who says his intention suffices as an intention for the whole month.” (Saheeh Ibn Khuzaimah no.1934)

Imaam Ibn al-Mundhir an-Neesaabooree said,

“There is Ijmaa (consensus ie unanimous agreement) that whoever made an intention every night to fast (for the following day), in the month of Ramadhan then his fast is complete.” (Kitaab al-Ijmaa no.123)

and there is no verbal intention as we often know the customary indian sub-content wording of such an intention “Wa-Bisaumin gaadhin Nawaitu….” there is absolutely no evidence or proof for this at all. And Allaah knows best.